Gene Pools, Selection, and Speciation- A14

Question 1

What is a species?

Answer 1

a group of similar organisms that can reproduce to give fertile offspring

Question 2

Explain the term population.

Answer 2

Group of organisms of the same species living in a particular area at a particular time - so they have the potential to interbreed.
Species can exist as one or more populations

Question 3

Define gene pool.

Answer 3

the complete range of alleles present in a population

Question 4

define allele frequency

Answer 4

how often an allele occurs in a population - normally given as a % of the total population.

Question 5

What is the Hardy-Weinberg Principle?

Answer 5

HWP is a mathematical model that predicts the frequencies of alleles in a population that won’t change from one allele to the next

Question 6

What are the conditions of the Hardy-Weinberg Principle?

Answer 6

-large population
-no immigration or emigration
-no mutations
-no natural selection
-random mating occurs(all possible genotypes can breed with all others)

Question 7

What are the Hardy-Weinberg Equations used for?

Answer 7

-used to estimate the frequency of particular alleles, genotypes and phenotypes within a population
-can also be used to test whether or not the HWP applies to particular alleles in particular populations
-i.e. to test whether selection or any other factors are influencing allele frequencies - if frequencies do change between generations in a large population then there’s an influence of some kind.

Question 8

What are the 2 different Hardy-Weinberg equations used to calculate?

Answer 8

1 for calculating allele frequency, 1 for calculating genotype and phenotype frequencies
-both were designed to be used in situations where a gene has two alleles

Question 9

What is the equation for allele frequency?

Answer 9

p+q=1
-p= dominant allele
-q= recessive allele
-total frequency for all possible alleles for one characteristic in a population is 1.0(100%)

Question 10

What is the equation for genotype frequency?

Answer 10

p^2 + 2pq+ q^2 = 1
-p=homozygous dominant(AA)
-2pq= heterozygous(Aa)
-q^2= homozygous recessive(aa)
-total frequency of all possible genotypes for one characteristic in a population is 1.0

Question 11

What is variation and what is it caused by?

Answer 11

-differences between individuals
-caused by genetic and/or environmental factors

Question 12

What is produced in intraspecific variation?

Answer 12

different phenotypes within a species

Question 13

How is genetic variation produced?

Answer 13

individuals of the same species have the same genes but may have different alleles

Question 14

What are reasons for genetic variation?

Answer 14

mutation, crossing over of chromatids, independent assortment and random fertilisation of gametes

Question 15

Which environmental factors can impact variation?

Answer 15

Composition of food, climate, or lifestyle

Question 16

Why two types of factor cause phenotypic variation?

Answer 16

Genetic, environmental

Question 17

What is evolution?

Answer 17

-The frequency of an allele in a population changes over time.
-occurs by genetic drift or by natural selection

Question 18

Explain the process of natural selection.

Answer 18

-organisms face selection pressures- these affect their chance of surviving e.g. predation, disease and competition
- members of the same species have different alleles, meaning some are better adapted to the selection pressure than others
-this means there are different levels of survival and reproductive success in a population
-individuals with a phenotype that increases their chance of survival are more likely to survive m reproduce and pass on their favourable alleles to the next generation
-this means a greater proportion of individuals will have the favourable alleles(and therefore phenotype) in the next generation. So they, in turn, are more likely to survive, reproduce, and pass on their alleles
-the frequency of beneficial alleles in the gene pool increases from generation to generation

Question 19

What does the effect of natural selection on allele frequencies depend on?

Answer 19

The selection pressures acting in the population.

Question 20

What are the 3 types of natural selection?

Answer 20

Stabilising selection, directional selection, disruptive selection

Question 21

What is stabilising selection?

Answer 21

-individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce(passing on favourable alleles)
-selective pressure at both ends of the distribution
-ultimately reduces the range of possible phenotypes by eliminating the extremes
-occurs when the environment isn’t changing

Question 22

What is directional selection?

Answer 22

-individuals with alleles for a single extreme phenotype are more likely to survive and reproduce(passing on favourable alleles)
-could be in response to environmental change

Question 23

What is disruptive selection?

Answer 23

-individuals with alleles for extreme phenotypes are more likely to survive and reproduce(passing in favourable alleles)
-opposite to stabilising selection as characteristics towards the middle of the range are lost
-occurs when the environment favours more than one phenotype

Question 24

What is speciation?

Answer 24

-development of a new species from an existing species
-occurs when populations of the same species become reproductively isolated

Question 25

Explain the term reproductively isolated.

Answer 25

Changes in allele frequency causes changes in phenotype, which means they can no longer interbreed to produce fertile offspring

Question 26

What type of speciation is reproductive isolation?

Answer 26

Allopatric speciation

Question 27

Describe allopatric speciation?

Answer 27

-new species is created when populations are isolated by geographical barriers -different selection pressures -mutations lead to variation which leads to change in allele frequencies -no gene flow so populations become reproductively isolated from each other -cannot reproduce and produce fertile offspring-speciation has occurred

Question 28

What speciation is reproductive isolation without geographical isolation?

Answer 28

Sympatric speciation

Question 29

What is sympatric speciation?

Answer 29

-occurs when random mutations within a population prevents individuals that carry the mutations from reproducing with individuals that don’t carry the mutation -occurs in the same population -rare- difficult for a section of a population to become completely reproductively isolated without being geographically isolated too

Question 30

What are the mechanisms of reproductive isolation and what are the types?

Answer 30

-occurs because of change in allele frequency therefore genotype and phenotype frequencies -prevent breeding due to: seasonal changes, mechanical changes, behavioural changes

Question 31

What is seasonal/temporal isolation?

Answer 31

-individuals develop different flowering or mating seasons, or become sexually active at different times of the year -organisms don't breed together, as they aren't reproductively active at the same time

Question 32

What is mechanical isolation?

Answer 32

changes in the size or function of genitalia can prevent successful mating, preventing individuals from producing fertile offspring

Question 33

What is behavioural isolation?

Answer 33

-a group of individuals may, for example, develop courtship rituals that aren't attractive to the rest of the group -prevents individuals from reproducing with each other, even if they could do so successfully

Question 34

How does speciation create diversity?

Answer 34

-diversity of life today is the result of speciation and evolutionary changes over millions of years -to start there was one population of organisms -the populations were divided and the new populations evolved into separate species -the new species were then divided again and the new populations evolved into more separate species- process repeated over a long period of time to create millions of new species

Question 35

What happens in evolution by natural selection?

Answer 35

-evolution by natural selection - selection pressures can change the allele frequencies of a population over time

Question 36

What happens in evolution by genetic drift?

Answer 36

- instead of environmental factors affecting which individual survives, reproduce and pass on their alleles, chance dictates which alleles are passed on

Question 37

How does genetic drift work?

Answer 37

-individuals within a population show variation in their genotypes(due to mutations producing alleles) -by chance, the allele for one genotype is passed on to more offspring than the others - so the number of individuals with the allele increases -if by chance the same allele on [assed on again and again, it can lead to evolution as the allele becomes more common in the population

Question 38

How can genetic drift lead to speciation?

Answer 38

-genetic drift can lead to differenced in allele frequency between two isolated populations -if enough differences in allele frequency build up over time, this could lead to reproductive isolation and speciation

Question 39

How does genetic drift effect population size?

Answer 39

-natural selection and genetic drift work together to drive evolution, but one process can drive evolution more than the other depending on the population size -evolution by genetic drift usually has a greater effect in smaller populations where chance has a greater influence -in larger populations any chance factors tend to even out across the whole population -genetic drift tends to cause the genetic diversity of a population to decrease -lack of genetic may make species less able to adapt to new selection pressures -so genetic drift can be a problem for small populations

Question 40

What are the different types of genetic drift?

Answer 40

-genetic bottlenecks -the founder effect

Question 41

What is a genetic bottleneck?

Answer 41

-an event causes a big reduction in population -reduces the number of different alleles in the gene pool and so reduces allele frequency and therefore genetic diversity -survivors reproduce and a larger population is created from a few individuals

Question 42

What is the founder effect?

Answer 42

- a few organisms from a population start a new colony(often due to migration, causing geographical isolation ) and there are only a small number of different alleles in the initial gene pool. -the allele frequency in the new population may be very different to allele frequency in the original population -sometimes leads to higher incidence of genetic disease